Both of the hearts we see repeatedly degrade and insult their 'owners.' It makes sense considering Joey and Sally probably have low self esteem.
Dick comparing his and Joey's relationship to "Batman and Robin" or "Superman and his dick" seems like a case of Metaphorgotten until you realize that Robin's first name is Dick.
Fridge Horror: Remember when Tiffany gets paired with Weenie at the end after losing the Old Snatch? It's depicted as a hilariously happy ending for both Tiffany and Weenie, but after that, Tiffany, despite being cisgender, is now a female with a penis and therefore technically a non-op transsexual. And remember how she had that reputation for really getting around? Now it's pretty unsafe for her to continue with that. If the wrong person sees her penis, she'll probably end up murdered due to "trans panic".
Like it says on the YMMV page, once you start thinking about the biology on display (especially when you start to consider things like sexual orientation), the ontological horror sets in to the point of distraction.